U.S. patent number 4,519,772 [Application Number 06/537,540] was granted by the patent office on 1985-05-28 for heating device fed with free-flowing fuel.
This patent grant is currently assigned to Webasto-Werk. W. Baier GmbH & Co.. Invention is credited to Bernd Mittmann.
United States Patent |
4,519,772 |
Mittmann |
May 28, 1985 |
Heating device fed with free-flowing fuel
Abstract
A heating device fed with free-flowing fuel and connected to an
on-board voltage source, in particular, a vehicle heater. The
heating device is equipped with a burner assembly which has a fuel
supply, a combustion air fan and a heating element which ignites a
fuel/air mixture after a preheating phase. During the preheating
phase, the combustion fuel fan is shut off or at least is operated
at less than the operating blower output. There is also a switching
device which automatically turns on or switches the combustion air
fan to its operating blower output after a preheating phase has
been completed. The switching device is designed as a
voltage-dependent time-function element, which presets a preheating
time dependent upon the magnitude of the on-board voltage and which
decreases the preheating time as the on-board voltage
increases.
Inventors: |
Mittmann; Bernd (Munich,
DE) |
Assignee: |
Webasto-Werk. W. Baier GmbH &
Co. (DE)
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Family
ID: |
6182015 |
Appl.
No.: |
06/537,540 |
Filed: |
September 30, 1983 |
Foreign Application Priority Data
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Dec 28, 1982 [DE] |
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3248412 |
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Current U.S.
Class: |
431/45;
237/12.3C; 237/2A |
Current CPC
Class: |
F24H
3/065 (20130101); F24H 9/2085 (20130101); B60H
1/2212 (20130101); B60H 1/2206 (20130101); F23N
2241/14 (20200101); B60H 2001/2253 (20130101); B60H
2001/2234 (20130101); F23N 2227/38 (20200101) |
Current International
Class: |
B60H
1/22 (20060101); F24H 3/02 (20060101); F24H
3/06 (20060101); F24H 9/20 (20060101); F23Q
009/08 () |
Field of
Search: |
;237/2A,12.3C ;126/11B
;431/45,43 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1125790 |
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Apr 1962 |
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DE |
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1124377 |
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Aug 1962 |
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DE |
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1143725 |
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Aug 1963 |
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DE |
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Primary Examiner: Bennett; Henry
Attorney, Agent or Firm: Sixbey, Friedman & Leedom
Claims
I claim:
1. In a heating device of the type fed with free-flowing fuel and
connected to an on-board voltage source, in particular, a vehicle
heating device with a burner assembly which includes a fuel supply,
a combustion air fan and a heating element to ignite the fuel/air
mixture after a preheating phase, during which at least the
combustion air fan is shut off or is operated at less than the
operating blower output, and with a switching device which
automatically turns on or switches the combustion air fan to its
operating blower output following completion of the preheating
phase, the improvement wherein the switching device comprises a
voltage-dependent, time-function element which presets a preheating
time for the heating element based on the magnitude of on-board
voltage applied thereto, and being operable to decrease preheating
duration as the on-board voltage increases.
2. Heating device according to claim 1, wherein a voltage/time
performance line of the time-function element is set in accordance
with a system of voltage-dependent, temperature/heating time
performance lines of the heating element in such a manner that the
temperature reached by the heating device within the preheating
time approximates an allowable maximum temperature, but does not
exceed same.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
The invention concerns a heating device fed with free-flowing fuel
and connected to an on-board voltage source, in particular, a
vehicle heating device with a burner assembly which includes a fuel
supply, a combustion air fan and a heating element which ignites a
fuel/air mixture after a preheating phase, during which the
combustion air fan is switched off or operated at less than the
operating blower output, as well as a switching device which
automatically turns on or switches the combustion air fan to its
operating blower output following completion of the preheating
phase. Heating devices of this type are already known (DE-PS Nos.
11 24 377, 11 25 790, and 11 43 725). The duration of the
preheating phase in these devices is set. Satisfactory ignition has
proven to be problematic in such equipment when the on-board
voltage changes. In the case of undervoltage, the temperature on
the glowing surface of the heating element, in particular, a glow
plug, can be so low that ignition of the fuel/air mixture is no
longer guaranteed. Should an overvoltage occur, the heating
element, e.g., its heating coil, could burn out.
The invention, thus, has for a principal object the creation of a
heating device which produces safe ignition, even when on-board
voltage varies, and in which the heating element is simultaneously
protected in a simple manner against damage by overvoltage.
This object is achieved, in accordance with a preferred embodiment
of the invention, by providing a device of the type mentioned
initially with a switching device that is designed as a
voltage-dependent time function element, which presets a preheating
time that is adjusted based on the magnitude of the on-board
voltage.
The invention is based on the fact that the temperature of the
heating element is a function of time, i.e., because of the
temperature dependence in the heating device, a period of time,
which will increase or decrease depending upon the actual voltage,
will pass before a predetermined operating temperature is reached.
By adjusting the preheating time, the temperature of the heating
element can consequently be limited to a value which will prevent
overheating of the heating element, even when the heating element
is selected in such a way that it ensures that a required ignition
temperature is achieved, even at the lower end of the expected
on-board voltage range.
In accordance with a further aspect of the invention, the
voltage/time performance line of the time-function element is,
preferably, adapted to the system of voltage-dependent temperature
heating time performance lines of the heating device in such a
manner that the temperature reached by the heating device within
the given preheating time approximates the maximum allowable
temperature of the coil, but does not exceed this temperature. This
guarantees a particularly high certainty of ignition being
obtained.
These and further objects, features and advantages of the present
invention will become more obvious from the following description
when taken in connection with the accompanying drawings which show,
for purposes of illustration only, a single embodiment in
accordance with the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a heating device in accordance
with the invention;
FIG. 2 is an illustration of the voltage/time performance line of
the time-function element of the heating element in the heating
device according to FIG. 1;
FIG. 3 is an illustration of the family of voltage-dependent
temperature/heating time performance lines of the glow plug of the
heating device according to FIG. 1; and
FIG. 4 is an illustration of a practical example of the
voltage-dependent time-function element of the heating device
according to FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The heating device illustrated in FIG. 1, which can, in particular,
be a vehicle heater, has a burner assembly 1 with an electric motor
2. Electric motor 2 drives the heating air fan 3, a combustion air
fan 4, a fuel pump 5 and a rotating atomizer 6. Combustion air is
suctioned in through a suction opening 7 and, along with the fuel
sprayed by rotating atomizer 6, is transferred to a combustion
chamber tube 8. Combustion chamber tube 8, along with a pot 9,
defines an exhaust channel 10, into which an exhaust opening 14
opens. A heating element, such as glow plug 12, is provided to
ignite the fuel/air mixture. The establishment of a flame in the
burner assembly 1 is monitored by combustion monitor 13, which has
a contact 25. The heat produced during operation of the heating
device is given off to the heating air conveyed by heating air fan
3 in a heating air channel 15.
After start switch 16 closes, electric motor 2 and glow plug 12 are
fed from battery 17, which constitutes an on-board voltage source,
via heating control device 18 which is shown schematically as a
block.
The arrangement described to this point is known.
In addition to the above, there is a voltage-dependent
time-function element 19 which sends a signal to its output a after
a delay period when voltage is applied to its inputs b and c; the
length of the delay time is dependent upon the magnitude of the
voltage at inputs b, c. According to FIG. 1, inputs b, c of
time-function element 19 are connected to the voltage supply
terminals of glow plug 12 via lines 20, 21, so that the voltage
supplied to inputs b, c is equal to the voltage at glow plug 12.
Output a of time-function element 19 is connected to heating
control device 18 via a line 22.
The heating device operates as follows: the start switch 16 is
closed to begin operation. The heating control device 18 sends
voltage to glow plug 12. The glow plug heats in accordance with the
temperature/heating time performance line. This performance line is
dependent upon the magnitude of voltage provided by battery 17.
Three such performance lines 26, 27, 28 are shown in FIG. 3 for
three different on-board voltages U.sub.1, U.sub.2, U.sub.3, which
are equal to, for example, 10 V, 12 V, and 14 V, respectively. The
temperature of the coil of glow plug 12 increases over time in
accordance with the corresponding performance line. At the same
time as the on-board voltage is applied to glow plug 12, this
voltage also appears at inputs b, c of time-function element 19.
Time-function element 19 is started. After a preheating time, which
is dependent upon the magnitude of the on-board voltage,
time-function element 19 sends a signal to heating control device
18 via its output a and line 22; this causes heating control device
18 to switch on electric motor 2 via a line 29. The relationship
between the voltage at glow plug 12 and preheating time T is
predetermined by time-function element 19, i.e., the time which
passes between the connection of voltage to time-function element
inputs b, c and activation of electric motor 2 due to the signal
received via line 22. This predetermined relationship can be seen
in FIG. 2, which, as an example, illustrates a corresponding
voltage/time performance line 30 of time-function element 19.
The performance line u=f (t), according to FIG. 2, was selected on
the basis of the temperature-heating time performance lines (e.g.,
performance lines 26, 27, 28 in FIG. 3), in such a manner that the
maximum permissible temperature T.sub.max of the coil of glow plug
12 will not be exceeded at the predetermined voltage-dependent
preheating time set by time-function element 19. A maximum
permissible preheating time t.sub.1, t.sub.2 or t.sub.3, according
to FIG. 3, is, thus, associated with each on-board voltage value;
the same, naturally, applies accordingly to intermediate values. It
is preferable for performance line 30, which reflects the
dependency of the preheating time upon the glow plug voltage, to be
adapted to the performance lines, e.g., performance lines 26, 27,
28 of glow plug 12, in such a manner that the glow plug can reach
or approximate, but not exceed, the maximum permissible temperature
T.sub.max within the preheating time set by time-function element
19. When electric motor 2 is switched on after the on-board
voltage-dependent preheating time has passed, fuel pump 5 and the
combustion air fan 4 begin to transport fuel and combustion air,
respectively. The fuel/air mixture formed by atomizer 6 is reliably
ignited by the glow plug, which has essentially been heated to
temperature T.sub.max. Thereafter, if desired, glow plug 12 can be
shut off when combustion monitor 13 responds. However, since the
heater coil is cooled by the combustion air flow produced by
combustion air fan 4, heating control device 18 can also be
designed so that glow plug 12 is left on, or operates as in U.S.
Pat. No. 4,350,288.
Should immediate ignition fail to occur for other reasons and in
spite of a sufficient plug temperature, thus requiring double or
triple preheating periods, time-function element 19 and/or heating
control device 18 should be designed such that a cooling phase of
sufficient duration follows each heating process before voltage is
again applied to glow plug 12. Otherwise, temperature T.sub.max
could be exceeded.
Although it was assumed, in the explanation of FIG. 1, that
electric motor 2 is dead in the preheating phase, it is also
possible, in accordance with a modified design, for the combustion
air fan to be operated at a reduced rpm during preheating; the
combustion air fan can then be switched to its operating blower
output using the signal from time-function element 19.
FIG. 4 shows a simple electromechanical design of a time-function
element 19. Time-function element 19 is formed by a thermo-relay
which has a heating coil 32 and a thermo-relay contact 33. When
started, voltage is applied to heating coil 32 via the inputs b, c.
The heating coil temperature increases more or less rapidly,
depending upon the magnitude of voltage applied. Once the switching
temperature is reached, relay contact 33 makes contact with a
stationary contact 34, sending a voltage signal from input b to
output a via contacts 33, 34; according to FIG. 1, this voltage
signal travels via line 22 to heating control device 18.
It is understood here that voltage-dependent time-function elements
other than the electromechanical time-function element 19, shown in
FIG. 4, may also be used; in particular, electronic time-function
elements of known design may also be used.
While I have shown and described a single embodiment in accordance
with the present invention, it is understood that the same is not
limited thereto, but is susceptible of numerous changes and
modifications as known to those skilled in the art, and I,
therefore, do not wish to be limited to the details shown and
described herein, but intend to cover all such changes and
modifications as are encompassed by the scope of the appended
claims.
* * * * *